Conventional PGA sockets comprise a base housing having a plurality of terminals arranged in the form of grid, and a slide plate having a corresponding plurality of through holes arranged in the same form of grid as the base housing. The slide plate is placed on the base housing, and the slide plate moves between an open position, in which the lead pins of the PGA package can be inserted in the through holes to reach the terminal mounts with an insertion force of zero or close to zero, and a locking position, in which the inserted lead pins are put in engagement with the terminals.
A cam member is provided along the rear edge of the base housing, which when activated, moves the slide plate between the open and locked position. In one embodiment, the cam member comprises a cam shaft that is rotated by means of an operation handle provided along the side portion of the socket (for example, see Japanese Unexamined Patent Publication No. Heisei 7-142134). Alternatively, the cam member is provided in a direction extending through the base housing and the slide plate. By rotating the cam member by means of a driver or the like, the handle is eliminated.
In the construction where the cam member is provided in an orientation extending through the base housing and the slide plate, the cam member is biased against the slide plate as the slide plate moves from an open to a locked position. In the condition where the lead pins and the terminals are placed for engagement with each other (the locked position), a reaction force by a resilient force of the lead pin acts on the cam member. The reaction force acting between the metallic cam member and the insulative slide plate, such as plastic or the like, contacting the cam member becomes greater as the number of lead pins increase. By this force, the portion of the slide plate which is in contact with the cam member can become deformed due to the fact that the insulative slide plate is more flexible that the cam member. This deformation can result in a convex deformation in the slide plate that can cause a degradation in the reliability of the PGA socket. This deformation can be amplified in those situations where the PGA packages are exchanged numerous times due to the large number of times that the PGA socket must be actuated between its open and locked positions.